The present invention relates generally to fuel injectors, and more particularly to common rail systems with the ability to produce separate pilot and main injections.
Common rail fuel injection systems have proven highly successful in diesel engine applications. Many of these injection systems use high pressure hydraulic fluid to actuate fuel injection. This has allowed great precision in controlling the initiation and termination of fuel injection, resulting in significant improvements in fuel efficiency and combustion burn quality over earlier systems. Furthermore, these systems have been shown to be highly versatile, allowing a great degree of control over injection rate shape.
The use of a common rail allows a simpler and more efficient fuel injection system design. A single pump can be used to pressurize fuel for injection. Using fuel itself as the actuation fluid can simplify the system further still. A separate delivery and return system for hydraulic fluid is no longer needed. Instead, the common rail is used to supply fuel for both combustion and injector actuation. However, these systems are not without problems. First, the use of high pressure fluid outside the injectors can result in fuel leakage to outside the system, creating serious safety concerns and compromising the systems"" mechanical integrity. Second, these injection systems often have difficulty producing separate pilot and main injections. Third, prior art injection systems often do not offer adequately controlled injection initiation and termination when smaller volume injections are desired, such as during idle speed operation. Fourth, the ability to reliably inject at different pressures in a single injection cycle is problematic.
The present invention is directed to overcoming one or more of the problems and limitations set forth above.
In one aspect of the present invention, a fuel injector is provided which includes an injector body, a fuel pressurization chamber, a nozzle chamber, a needle control chamber, a needle control spill outlet, a fuel inlet, and a nozzle outlet. A pressure intensifying pumping element is provided which has a large hydraulic surface exposed to fluid pressure in the actuation fluid cavity, and a small hydraulic surface that is exposed to fluid pressure in the fuel pressurization chamber. The needle control chamber is fluidly connected to the fuel inlet and the needle control spill outlet. A needle valve is positioned in the injector body and includes a closing hydraulic surface that is exposed to fluid pressure in the needle control chamber. A flow control valve is attached to the injector body that is moveable between a first position in which the actuation fluid cavity is open to the fuel inlet, and a second position in which the actuation fluid cavity is closed to the fuel inlet.
In another aspect, a fuel injection system is provided which includes a source of intermediate pressure fuel, a pressure intensifying pumping element, a flow control valve, and a low pressure reservoir. The fuel injection system also includes at least one fuel injector having a needle valve, and an injector body defining a needle control chamber fluidly connected to a needle control spill outlet and a fuel inlet, and a nozzle outlet. An intermediate pressure supply line extends between the source of intermediate pressure fuel and the fuel inlet. A low pressure vent line extends between the needle control spill outlet and the low pressure reservoir. A pressure release valve is positioned in the vent line and has a first position in which the vent line is closed, and a second position in which the vent line is open.
In still another aspect, a method of injecting fuel is provided which includes the steps of injecting fuel at a high pressure at least in part by fluidly connecting a nozzle chamber of a fuel injector to a source of intermediate pressure fuel, and injecting the fuel at a high pressure at least in part by exposing a pressure intensifying element to the source of intermediate pressure fuel.